Test the normality (devided with 6 sub-groups) then use an appropriate statistical test to solve the problem.

Serum estradiol is an important risk factor for breast cancer in postmenopausal women. To better understand the etiology of breast cancer, serum-estradiol samples were collected from 30 premenopausal women (at about the same time period of the menstrual cycle) of whom 12 were Caucasian and 18 were African American. Data were collected on both serum estradiol as well as body mass index (IBM), which is an important measure of overall obesity:

BMI	Status
Below 18.5	Underweight
18.5 24.9	Normal weight
25.0 29.9	Overweight
30.0 and above: - 30 to < 35 - 35 to < 40 - 40 or higher	Obese: - Class 1 - Class 2 - Class 3

Is there a difference between mean serum estradiol between women having BMI < 25 and women having BMI >= 25 based on the data shown in the below table?

ID	Serum estradiol (pg/mL)	Estradiol rank	BMI	Ethnic group (0 = Caucasian, 1 = Afr. Ame.)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30	94 54 31 21 46 56 28 29 12 14 28 25 35 43 22 71 43 35 42 50 44 41 28 65 42 31 35 91 55 34	25 10 9.5 5 18 21 3 4 1 2 3 7 12 15 6 23 16 12 15 19 17 14 8 22 17 9.5 12 24 20 14	18.9 19.7 20.7 23.4 23.3 25.1 35.6 26.2 22.3 20.4 26.1 21.7 20.0 32.5 21.0 21.8 32.7 23.6 24.7 23.2 33.9 20.6 24.7 26.3 33.1 20.1 22.5 29.1 26.4 27.8	0 1 0 1 1 0 1 1 1 0 1 0 1 1 1 0 1 1 1 1 1 0 0 0 0 1 1 0 1 0